Engine diesels, and it's jerking while running!

Hello to the community...

I'm having a problem with my Ford Mondeo 1.8 TD.

I'm sorry, I don't know if this is the right forum for this.

As I've already mentioned, I have a problem: the engine starts perfectly in a cold state, but once it's warm, it starts to jerk.
It feels like (User) is taking their foot off the gas and then putting it back on.
Man drives at approximately 140 km/h, then reduces to 137 km/h, and immediately accelerates back up to 142 km/h... etc.

The next problem is that when it is turned off, and then restarted after 15 minutes, it starts up, but after 10-15 seconds, it dies again. And then it is barely possible to restart it, taking about 5 minutes.

does anyone have an idea?

Regarding the car: Ford Mondeo 1.8 l TD, manufactured in 10/95, Engine RFN, 88 hp. It does not have any Electronic ESP.

Thank you for your help.

Best regards, Michael